Nowadays the life is increasingly rich and various. A bag or case, in particular a movable bag or case having universal corner rollers, is usually necessary at work, in sports, in recreation or the like. However, when the work or travel is finished, the bag shall be packed in a proper way, but the bag with rollers is hardly to be fixed. When a user goes outdoors for sports, for instance, going fitness, golf, swimming or the like, which does not require too much things, and the user doesn't want to carry a bag by hand, the user can take a bag with rollers for an easy trip. Now there are bags or cases with universal corner rollers that are fixed on the bag body or case body. No matter how many degrees the rollers rotate, they are not detachable. Such bags or cases have bad adaptability during the application. Besides, rollers are worn out most quickly among all of the components of a bag or case. When the other parts of the bag or case are still in normal state, but the worn rollers are out of use, it would be impossible that the user replaces the worn rollers with new ones by himself, since the rollers cannot be detached.
Moreover, a detachable roller means in a snap-fit manner is known in the prior art, wherein the snap-fit arrangement should be designed extremely firm, for preventing the rollers from falling off unintentionally under an external load. It usually requires tools or a great effort to loose the snap-fit arrangement. And the firmness of the snap-fit arrangement is reduced with the times of the actuation to the snap-fit arrangement.